German President Frank-Walter Steinmeier said he would run for a second term of office next year, implicitly gambling that the likely winners of September's national election would not turf out a sitting national figurehead from a different party.

Steinmeier, 65, a Social Democrat (SPD) and former foreign minister, was appointed president under Chancellor Angela Merkel's previous conservative-SPD coalition government.

But the SPD is running a distant third in election polls, meaning it is unlikely to play a role in Germany's next government. If so, Steinmeier would be relying on a German convention of respect for sitting presidents to hold on to office.

"I would like to run for a second term as president," he told a Friday news conference at Schloss Bellevue, his official residence in Berlin, adding that he wanted to help "heal the wounds" left by the COVID-19 pandemic.

Germany's president has few powers, but is typically a senior politician who, once elected by the lower and upper houses of parliament, must seek to unify and set a high moral tone for the nation.

Polls suggest either the conservatives or the Greens will dominate the Bundestag (lower house) after the election.

SPD allies backed him following the announcement, though Bavarian Premier Markus Soeder, a conservative, said any decision on whom to endorse would be taken after the election.

While his predecessor Joachim Gauck, a Lutheran pastor, was hailed for his bravery as a civil rights activist in former Communist East Germany, other presidents have drawn controversy.

Horst Koehler resigned in 2010 after being accused of advocating "gunboat diplomacy" during a visit to troops in Afghanistan. Heinrich Luebke resigned in 1969 over allegations that he had used slave labour and built concentration camps during the World War Two Nazi regime.

A pro-European, Steinmeier has been criticised for perceived leniency towards an aggressive Russia. Earlier this year, he said Germany owed it to Russia to complete the controversial Nord Stream 2 pipeline because of the suffering Nazi Germany had inflicted there in World War Two.

Critics responded that much of that suffering had been borne by Soviet successor states Ukraine and Belarus. Ukraine strongly opposes the pipeline under the Baltic, which would cut it out of lucrative gas transit business.